1. Field of the Invention
The present invention relates to a wireless LAN communication system having an infrastructure mode and an ad-hoc mode. Wherein, in the infrastructure mode, each station communicates with another station via an access point, while, in the ad-hoc mode, direct communication is performed between two stations located near each other. More particularly, the present invention relates to a wireless LAN communication system as follows. In wireless LAN communication system, when one station is capable of communicating directly with another station without needing an access point, communication is performed in the ad-hoc mode. And when communication in the ad-hoc mode is impossible, communication is performed in the infrastructure mode. In such cases, the communication mode should be automatically switched between the ad-hoc mode and the infrastructure mode depending on the status.
2. Description of the Related Art
Wireless LANs generally have an infrastructure network and an ad-hoc network. The infrastructure network is used for communications between stations via access points, and the ad-hoc network is used for direct communications between stations located near each other.
In conventional wireless LAN communication systems of the type described above, a wireless terminal serving as a station has information indicating other wireless terminals with which ad-hoc communication is possible. When a wireless terminal communicates with another wireless terminal that is registered in the cash memory, the ad-hoc mode is automatically selected at the start of the communication, and thus communication is performed without passing through an access point (Japanese Unexamined Patent Publication JP-A No. 7-303105).
At the start of communication, a wireless station examines a database to determine whether a station with which to communicate is registered in the database and whether communication in the ad-hoc mode is possible. In the case in which the station with which to communication is not registered in the database, it is tested whether communication in the ad-hoc mode is possible. If it turns out that communication in the ad-hoc mode is possible, the station is registered in the database, and a communication channel is established. If communication in the ad-hoc mode is impossible, the communication mode is switched into the infrastructure mode, and communication procedure is started.
When a station with which to communicate is already registered in the database, communication procedure is started in the ad-hoc mode and communication is established. However, if the situation has changed into a state in which communication in the ad-hoc mode is no longer possible, the communication mode is switched into the infrastructure mode, and communication procedure is started. In a case in which communication in the ad-hoc mode becomes impossible in the middle of communication because of movement of a station, the station automatically switches the communication mode into the infrastructure mode to try to maintain communication.
In the conventional wireless LAN communication system, although a wireless station can automatically switch the communication mode from the ad-hoc mode into the infrastructure mode, automatic switching from the infrastructure mode into the ad-hoc mode is impossible. That is, the capability of automatic switching of the communication mode is very limited.
This is because communication procedure is started in the ad-hoc mode regardless of information recorded in the database.